ES2702700T3 - Steel continuous casting method - Google Patents

Abstract

A method of continuous casting of steel in which a slab having a rectangular cross section is molded at the same time as vibrating the slab with a liquid core by arranging at least one pair of vibration impact equipment on both surfaces of short side of the slab and continuously impacting on said surfaces, characterized in that: a vibration energy, a distance between the shafts of the adjacent guide rollers and a thickness of the liquid core are adjusted, in such a way that the impact of the side surface short causes a displacement curve δ (x) of the long side slab surface in the slab thickness direction as defined by the following formulas (1) and (2) to intersect with a straight line δ (x) = 0.10 mm at two locations, and a distance from the intersection furthest from the coordinate origin in the slab thickness direction, representing the distance from an impact position on the short side of the slab, it is at least 200 mm; y is impacted on the short side, where each symbol in formulas (1) and (2) is indicated as follows, x is a distance (mm) in the slab thickness direction, being the impact position at the short side of slab 0, δ (x) is a displacement (mm) of the slab surface in the slab thickness direction at position x, δmax is the maximum displacement (mm) in the slab thickness direction, ΔR is a distance between the shafts of the adjacent guide rollers (mm) at the position where it impacts on the short side, E is the impact energy per side per segment (J), and t is a liquid core thickness of the slab at position impact on the short side of the slab (mm), in which the constants are defined as E0 = 39 (J), ΔR0 = 245 (mm), t0 = 26 (mm), and L0 = 0.114 (mm).

Description

DESCRIPTION

Steel continuous casting method

Technical field

The present invention relates to a method of continuous casting of steel that molds while causing a vibration in a slab impacting a specific surface of the slab in a state containing a liquid core.

Background of the technique

The internal defects that are macro segregation, called central segregation, V-shaped segregation or inverse V-shaped segregation, are easily formed in the central part in the thickness direction and in the vicinity of it for the slab that is molds by continuous casting. The central segregation is an internal defect that appears due to elements of solute that are easily segregated (hereinafter referred to as "segregation elements"), such as C, S, P and Mn, which are enriched in the end of the liquid crater of a slab and the V-shaped segregation and the reverse V-shaped segregation are internal defects that appear due to these segregation elements that are enriched in the vicinity of the liquid crater end of the slab in the form of V or in the form of an inverse V.

In a product that is manufactured by hot processing such as a slab including these macro segregations, a decrease in toughness, a cracking induced by hydrogen, and the like easily occur, and, in addition, cracking easily occurs when the produce a final product cold rolling such product.

The mechanism of formation of segregation in a slab is considered to be as follows. Specifically, as the solidification proceeds, the segregation elements are enriched between the dendrite arms of the columnar dendrite, which are a solidification structure. The molten steel in which these segregation elements have been enriched (hereinafter also referred to as "molten steel enriched in solute") overflows between the dendrite arms of the columnar dendrite due to the amount of solidification shrinkage during solidification, the expansion of the so-called domed slab, or the like. The solute-enriched molten steel that overflows in this way flows to the liquid crater end of the slab to solidify in a condition as it is, thereby forming a region enriched with the segregation elements. The region enriched with the segregation elements formed in this way is segregation.

Preventing the movement of the molten steel enriched in remaining solute between the dendrite arms of the columnar dendrite, preventing this molten steel enriched in solute from concentrating locally, and the like, are effective measures to prevent the segregation of the casting slabs, and so far, various methods have been proposed.

Next, in the patent literature 1, the present inventors have proposed a method of continuous casting of steel, when casting a slab with a rectangular cross section, which is molded while causing a vibration in the slab by continuously impacting the short side of the rectangular cross section thereof, using impact vibration equipment disposed in at least one location on said short side, including the slab a liquid core having a solid fraction of 0.1 to 0.9 in the part central in the thickness direction.

Furthermore, in the patent literature 2, the present inventors have proposed a method of continuous casting of steel, when a reduction lamination is carried out along the extraction direction for a slab with a rectangular cross section, the slab containing a Liquid core, with a plurality of pairs of guide rollers that are used for the reduction laminate, is molded at the same time as vibrations are caused in the slab when rolling continuously impacting at least one location on the slab surface within a region where the reduction run is made along the direction of extraction.

According to these methods, a columnar dendrite is made in the growth stage to be broken by the impact vibration in a slab, so it is possible to avoid the generation of the columnar dendrite. In addition, cavities / spaces are generated after premature cooling emerges in an equiaxial structure, and segregation occurs inside the cavities / spaces; however, these cavities break on impact. As a result, the equiaxial structure grows in high density and, therefore, molten steel enriched in solute can be manufactured to finely disperse between the solidified grains, and segregation is reduced, such as central segregation, segregation in the form of V and the segregation in reverse V shape, so it is possible to obtain a slab with good interior quality.

List of citations

Patent bibliography

Patent Bibliography 1: Japanese Patent No. 3835185

Patent Bibliography 2: Publication of Japanese Patent Application No. 2003-334641

Summary of the invention

Technical problem

As an internal defect in addition to segregation, there is a central porosity. The central porosity represents the fine pores generated around the end portions widthwise in the central part in the thickness direction thereof which is the final solidification point, due to the solidification contraction, while the molten steel is solidifies in continuous casting and due to thermal contraction by cooling after solidification. It has been required to reduce the segregation as well as the central porosity in order to improve the internal quality of the cast iron. In addition, it has been required to establish the appropriate vibration conditions by investigating the detailed relationship between vibration conditions of the slab by impact and the quality in the central part of the slab, to improve the efficiency of the continuous casting.

The present invention has been made in view of the aforementioned problems, and the object thereof is to provide a method of continuous casting of steel which can efficiently obtain slabs with good interior quality without segregation and / or without center of porosity, by the impact of a slab in suitable conditions to cause a vibration in it.

Documents JP 2006-110620, JP 2002-273554 and AT 270 101 B disclose the characteristics of the pre-characterizing part of claim 1.

Solution to the problem

The present inventors have studied the methods of continuous casting of steel to efficiently obtain slabs with good interior quality without segregation and / or without center of porosity, and obtain results in the following (A) and (B).

(A) When impacting a slab with liquid core at a position on the short side slab surface of the rectangular cross section thereof, if a region in which the displacement produced from the slab in the thickness direction thereof is at minus 0.10 mm, and a maximum distance of said region in a direction normal to the short side, ie, in the slab thickness direction, is at least 200 mm away from the impact position, the separation in the interior of the slab.

(B) The displacement produced from the slab in the direction of thickness due to impact varies as a function of the distance between the trees of the adjacent guide rollers, the impact energy and the thickness of the liquid core in the impact position of the slab.

The present invention has been made based on the results mentioned above, and consists of a continuous casting method of steel according to the following first and second aspects.

According to a first aspect, in a steel continuous casting method, when a slab having a rectangular cross-section is molded at the same time a vibration is caused in the slab with a liquid core by arranging at least a pair of equipment vibration impact on both surfaces of short side of the slab and impacting continuously on said surfaces, the method is characterized by: a vibration energy, a distance between the trees of the adjacent guide rollers and a thickness of liquid core, such so that the impact of the short side surface causes a displacement curve 8 (x) of the long side slab surface in the thickness direction as defined by the following formulas (1) and (2) to intersect with a straight line8 (x) = 0.10 mm at two locations and a distance from the intersection farthest from the origin of coordinates in the slab thickness direction, which rep shows the distance from an impact position on the short side of the slab, is at least 200 mm; and it hits the short side.

5 (x) = expj - 1.5 x {ln (x / (200x (AR / AR0) ° 587))} 2] * 5max (1)

6max = L0 x (E / E0) 05 * (AR / AR0) x (t / t0) 0446 (2)

In this case, each symbol in formulas (1) and (2) is indicated as follows:

x is a distance (mm) in the slab thickness direction, the impact position being on the short side of slab 0,

8 (x) is a displacement (mm) of the slab surface in the slab thickness direction at the x position,

8max is the maximum displacement (mm) in the slab thickness direction,

AR is a distance between the trees of the adjacent guide rollers (mm) in the position where the short side impacts,

E is the impact energy per side per segment (J), and

t is a liquid core thickness of the slab in the impact position on the short side of the slab (mm), where Eo is 39 (J), ARo is 245 (mm), to is 26 (mm), and Lo is 0.114 (mm).

According to a second aspect, in the steel continuous casting method as described in the first aspect, by using the same phase of time to cyclically impact the opposite left and right short sides of the slab, the displacements 8 (x ) generated by impacting the left and right short sides, respectively, are combined with each other, and the resulting displacement 8 (x) combined in this way is at least 0.10 mm over the entire width of the slab at the impact positions.

Advantageous effects of the invention

According to the present invention, since the vibration that has the displacement of the long side surface of slab, caused by the impact of the short side of slab, of at least 0.10 mm can be generated in a wide range of the slab, segregation and / or central porosity is reduced, so that a slab that excels in interior quality can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a view showing a continuous casting machine that can adopt a continuous casting method of the present invention and an impact vibration equipment arrangement, where (a) shows a side view of the continuous casting machine, and (b) shows a plan view of a part in which the impact vibration equipment of the continuous casting machine is installed;

Figure 2 is a cross-sectional view of a slab, showing the sampling positions of the samples to calculate the specific volume of the central porosity;

Figure 3 is a graph showing a relation between the impact energy per side per segment and the reduction in the specific volume of the central porosity in an end part widthwise of the slab; Figure 4 is a schematic view of a vibration model according to the impact of a slab with a liquid core part, where (a) shows a plan view, and (b) shows a view from the extraction direction;

Figure 5 is a graph showing a relationship between the distance of a short side impact position and the displacement of the long side surface of slab in the thickness direction;

Figure 6 is a graph showing a relation between the maximum displacement 8 max in the slab thickness direction and the reduction in the specific volume of the central porosity, - AV p;

Figure 7 is a graph showing a relationship between the impact energy per side per segment and the achievable distance of vibration;

Figure 8 is a graph showing a relationship between the impact energy per side per segment and the reachable distance of vibration, and showing the influence of the distance between the trees of the adjacent guide rollers; Y

Figure 9 is a graph showing the influence of impacting each short side surface that is one end across the width of the slab.

Description of the realizations

Hereinafter, the reasons for specifying the method of the present invention as above and the preferred embodiments of the method of the present invention will be explained.

The present inventors have analyzed the effects of vibrations by performing continuous casting experiments while causing vibrations in a slab by impact, thereby investigating the influence of vibrations on the inner quality of a slab, as described below .

1. Relationship between internal quality of slab and impact energy.

1-1. Experimental conditions of laundry

Figure 1 is a view showing a continuous casting machine that can adopt a continuous casting method of the present invention and an impact vibration equipment arrangement, where (a) shows a side view of the continuous casting machine, and (b) shows a plan view of a part in which the impact vibration equipment of the continuous casting machine is installed. The continuous casting machine shown in the same figure is of the vertical bending type and includes impact vibration equipment for the slab of wash.

Molten steel 4 cast from a tundish (not shown) in a mold 3 through an immersion nozzle 1 is cooled by mold 3 and a spray of water injected from the secondary cooling spray nozzles (not shown) below it, whereby a solidified surface area 5 is formed to be a slab 7. With the liquid core remaining inside it, the slab 7 is removed while being supported by the guide rollers. The meniscus, which is a surface 2 of the molten steel 4, is shown in the mold 3 of Figure 1. The guide rollers 6 are grouped into a plurality of segments and arranged (not illustrated). Next, two pairs of vibration impact equipment 8 are installed at a site downstream of the roller guide 6 with respect to the extraction direction, each pair being arranged in each segment comprised of the guide rollers to impact the short sides of the slab 7. Each impact vibration equipment 8 has a drive mechanism 10 and an impact effect block 9 mounted on a front leading end portion thereof.

In the present continuous casting experiments, a mold has been used for a slab having a thickness of 300 mm such as the mold 3. In order to examine the influence of the impact vibration along a widthwise direction , a wider width slab 2300 mm wide has been used as the slab 7. In the casting experiments a steel class of the following chemical composition was adopted for use in thick plates. Specifically, it was a kind of steel that includes, in bulk, 0.05 to 1.00% carbon, 0.04 to 0.60% silicon, 0.50 to 2.00% manganese, no more than 0.020% phosphorus and not more than 0.006% sulfur, the remainder being iron and unavoidable impurities.

The casting speed was set at 0.58 to 0.61 m / min, and the amount of secondary cooling water was adjusted to 0.62 to 0.73 liter / kg steel. The average temperature of the molten steel in the tundish was kept substantially constant with an overheating of AT in the range of 30 to 50 ° C. The AT is the difference between the actual temperature of the molten steel and the liquid temperature of the molten steel.

The two pairs of vibration impact equipment 8 were disposed, respectively, at the 22.5 m and 24.0 m positions downstream of the meniscus 2 in the mold 3 with respect to the extraction direction, respectively, with each midpoint longitudinal of the impact effect block 9 along the direction of extraction that is used as a measured point. For the impact effect blocks 9 of the vibration impact equipment 8, the length of an impact effect surface along the extraction direction was 1155 mm, the height in the vertical direction was 135 mm and the mass was 500 kg. An air cylinder equipment was used in the drive mechanism 10 of the vibration impact equipment 8. The frequency of the impact vibration on the short sides of the slab 7 was set at 4 to 6 Hz, ie 4 to 6 impacts per second.

When impacting on the short side of the slab, the columnar dendrite in the growth stage is manufactured to break, which can prevent the generation of the columnar dendrite. In addition, after premature cooling occurs in the equiaxed structures, cavities / spaces are generated, thereby causing segregation in the cavities. However, these cavities are destroyed by the impact. As a result, an abundant equiaxial structure at high density is produced, and therefore the molten steel enriched in solute can be fabricated to finely disperse between solidified discrete grains, and segregation and / or central porosity can be reduced.

The solid fraction in the central part in the thickness direction of slab 7 was calculated from the calculation of unidirectional heat transfer in the slab thickness direction with the casting speed and the amount of cooling water being the main parameters, and depending on the result thereof, conditions were obtained to achieve a predetermined solid fraction in the central part in the direction of thickness in an impact position. Subsequently, the continuous casting was carried out under the conditions while the short sides of the rectangular slab were impacted.

1-2 Estimation of the internal quality of the slab.

The estimation of the internal quality of the slab obtained by the continuous casting carried out at the same time that the impact on the short sides of the rectangular slab was made by estimating the state of the central generation of porosity.

1-2-1 Method for estimating the generation status of the central porosity

The generation state of the central porosity was estimated by the following method. Taking into account the precision of the specific gravity measurement and the sample for the calculation of the specific volume of the central porosity sampled from a slab, a rectangular solid with a length of 50 mm was made (thickness direction of the slab) , a width of 100 mm (direction of slab thickness), and a thickness of 7 mm (direction of slab extraction), and the surface finish was made based on the JIS regulations for the surface roughness in the surface roughness represented by the triangular mark VW: the maximum surface roughness of 3.2 | im. The generation state of the central porosity was estimated from the specific volume of the central porosity calculated from the density in the central part in the thickness direction, while the density in a quarter-thick position in the direction thickness (hereinafter also referred to as the "quarter-thickness position") from the slab surface which is a reference, since there should not be a significant generation of central porosity there. The specific volume of the central porosity Vp was defined by the following formula (1) using the average density p0 at the thickness position of a quarter and the average density p in the central part in the thickness direction.

V p = 1 / p - l / p 0 (1) Figure 2 is a cross-sectional view of a slab, showing the sampling positions of the samples to calculate the specific volume of the central porosity. A region representing an end portion widthwise in cross section that is normal to the direction of extraction of the slab, is shown in a fragmented manner in Figure 2. The average density p0 in the thickness position of a quarter of the slab it was calculated by collecting a sample 7a at one location in each end part across the width of the slab, totaling two, and measuring and averaging the respective densities. The average density p in the central part in the thickness direction was calculated by collecting the samples 7b, 7c and 7d in three locations in one end part widthwise of the slab, totaling six, and measuring and averaging the respective densities. The sampling positions are close to the short side of the slab, in which the positions at which samples 7a to 7d were collected were such that samples 7a and 7b are 190 mm from the short side of the slab, samples 7c are at 320 mm thereof, and the samples 7d are 425 mm from it, which represents the distance from each longitudinal center of the sample to the short side of the slab, respectively.

Next, based on the specific volume of the central porosity Vp ⁰ of an impact-free slab and the specific volume of the central porosity Vp ¹ of a slab subject to impacts, the reduction in the specific volume of the central porosity, -AVp , was defined by the following formula (2).

1-2-2 Results of estimation of the state of generation of the central porosity

Figure 3 is a graph showing a relationship between the impact energy per side per segment and the reduction in the specific volume of the central porosity in an end-to-width part of the slab. In the same graph, we calculated the reduction in the specific volume of the central porosity, -AVp, for each slab subjected to impacts with different impact energies, and represented graphically. From the relationship shown in the same graph, a relationship was confirmed in which the specific volume of the central porosity is reduced in an end part to the slab width when the impact energy E per side per segment exceeds 25 J. When calculating the regression equation for the relationship between the impact energy E per side per segment and the reduction in the specific volume of the central porosity, -AVp, in the same graph, the following formula (3) was obtained.

-AVp [cm3 / g] = 0.0049347xE [J] - 1,297487 (3) Next, the result is obtained from Figure 3 that a reducing effect in the central porosity at the level of -AVp = 0.57 x 10.4 cm3 / g in terms of specific volume of the central porosity when the impact energy E is 39 J. In addition, as a result of observing the macro structure, a tendency was recognized that granular segregation it is less for the slab subjected to impacts than the slab free of impacts.

2. Generalization of the relationship between the internal quality of the slab and the impact energy.

Based on the above result, the present inventors further studied the generalization of the aforementioned result in relation to the impact on the short sides of the slab of rectangular cross-section.

Figure 4 is a schematic view of a vibration model according to the impact of a slab with a liquid core part, where (a) shows a plan view, and (b) shows a view from the extraction direction. In the same figure, the solidified surface area 5 of the slab 7 is in a state of being restricted by the guide rollers 6. In this state, the short sides of the slab 7 are impacted by the impact vibration equipment 8.

The shape of the impact effect block 9 of the vibration impact equipment 8 was made in the form of a rectangular solid with a length a of 1200 to 1600 mm along the direction of extraction, the thickness c of 140 mm, and a width b of 200 mm in the thickness direction of slab. In addition, the slab 7 measures a width of 2300 mm and a thickness of 300 mm. Using a three-dimensional model of this type, a numerical analysis was performed for the displacement of the impact surface (long side surface) of the slab 7 by vibration.

The present inventors obtained from the numerical analysis results of the surface displacement of the slab 7 caused by the impact vibration in such a way that the maximum displacement 8 max of the slab in the thickness direction was substantially equal to the value 8 ^x = ²⁰⁰ mm in a position of 200 mm, in a normal direction towards the short side (ie the slab thickness direction), away from the impact position on the short side.

In addition, the present inventors found that, according to previous studies on the relationship between the variable interval L of displacement in a position on the interface between liquids and solids and various factors that have an effect on them, the variable interval L of the displacement within the vibration region it was adjusted by the impact energy E caused by the impact effect block, and that the relation thereof can be described by the following formula (a). Hereinafter, each symbol with the subscript 0 indicates a representative condition.

Further, it was found that the influences in the variable range of displacement by the distance AR between the adjacent guide roller shafts and the liquid core thickness t of the slab in the impact position on the short side of the slab can be adjusted independently, and the variable range of the displacement of the long side surface in the slab thickness direction at a position of 200 mm, in a normal direction towards the short side, from the impact position on the short side changes substantially in direct proportion to AR . Based on this knowledge, the following formula (b) extended from formula (a) was obtained as an equation for estimating the variable interval L of the displacement.

In this case, f (t, t0) represents the effective term of the thickness of the liquid core of the slab. When it was assumed that f (t, t0) was proportional to the exponent of the dimensionless value t / t0, the following formula (c) was obtained from the simulation results of the experiment as an example of the function f.

Next, substituting the formula (c) in the formula (b), the following formula (4) is finally obtained as an equation for estimating the variable interval L of the displacement (= 8max).

In this case, each symbol in the previous formula (4) indicates the following various quantities:

E: impact energy per side per segment (J);

AR: distance between the trees of the adjacent guide rollers in an impact position on the short side (mm); Y

t: thickness of the liquid core of the slab in an impact position on the short side of the slab (mm).

In addition, E ⁰ , AR ⁰ and fe are numerical values of the condition in which the central porosity reduction effect of E, AR, and t is the largest, respectively, and L ⁰ is a condition representative of the maximum displacement in the thickness direction of the slab when the effect of central porosity reduction is greatest, and each is the constant in the following way (5). Hereinafter, these conditions are also referred to as condition (5).

The present inventors found that, when the displacement 8 (x) in the thickness direction of the slab surface (i.e., the long side) in a position that is in a normal direction towards the short side of the slab and away from the impact position on the short side of the slab a distance x, calculated by the numerical analysis, is approximated according to the logarithmic normal distribution, it is possible to generalize as the following formula (6), using the 8max of the previous formula (4) .

Figure 5 is a graph showing a relationship between the distance from a short side impact position and the displacement of the long side slab surface in the thickness direction. The horizontal axis on the same graph is the distance x from the impact position on the short side of the slab in a normal direction to the short side, and the vertical axis is the dimensionless displacement in the slab thickness direction of the surface of the slab (dimensionless value where 8 (x) is divided by 8max to allow the maximum displacement to be one (1)). In the same graph, the open circle marks indicate the calculated values according to the numerical analysis, and the solid circle marks indicate the approximate values according to the logarithmic normal distribution. It is evident from the results shown in the same graph that the values calculated according to the numerical analysis are accurately approximated by the logarithmic normal distribution.

3. Relationship between the internal quality of the slab and the displacement of the slab surface by impact

Figure 6 is a graph showing a relation between the maximum displacement 8 max in the slab thickness direction and the reduction in the specific volume of the central porosity, - AV p. The relationship shown in the same graph was prepared looking for the relation between 8max and - AVp from the formula (3) and the formula (4) while setting AR as 245 (mm) and t as 26 (mm) adopting the condition (5). For the liquid core thickness t of the slab in the impact position on the short side of the slab, the liquid core thickness at the entrance of the segment in which the impact vibration equipment 8 is disposed was calculated from the analyzes of conduction and solidification of heat for the case of the casting speed of 0.7 m / min to be used.

The present inventors have discovered, from the results of Figure 6 that, when 8max is at least 0.10 mm, the specific volume of the central porosity decreases for a slab with a thickness of 300 mm and a width of 2300 mm.

In addition, the present inventors have advanced the study on the relationship between the inner quality of a slab and the displacement of the slab surface by impact, and have discovered that, when 8max is at least 0.10 mm and the distance x that produces 8max from the short side is at least 200mm, or alternatively, the distance x that produces 8max is less than 200mm and the displacement 8 (x) at x = 200mm is at least 0.10mm, the segregation and the central porosity can be realized so that they diminish in a wide interval of the interior of the slab, and the inner quality of the slab can be improved. Furthermore, although the present continuous casting experiments were performed by installing two pairs of impact vibration equipment, it was confirmed that an effect of improvement of the inner quality of the slab is obtained even in the case of a pair or three or more pairs of similar to the case of two pairs of vibration impact equipment.

4. Relationship between the impact energy and the achievable distance of impact vibration

Solving the above formula (6) for x, the following formula (7) is obtained as a function of the displacement 8 in the thickness direction of the slab and the distance between the trees of the adjacent guide rollers of AR in the impact position in the short side surface.

X - 200x (AR / ARo) ° 587 * exp [{- ln (8 / 8max) / l, 5} ° 5] (7)

Figure 7 is a graph showing a relationship between the impact energy per side per segment and the achievable distance of the vibration. The maximum value x * of the distance x of a region in which the displacement 8 in the direction of slab thickness due to impact is at least 0.10 mm, as it is from the impact position on the short side of the slab in a normal direction to the short side, is defined as the achievable distance of the vibration. The solid circle mark on the same graph is the result, in the case of impact while adopting condition (5), which configures the thickness of the slab as 300 mm, the impact energy E per side per segment for the short side of the slab as 40 J, which shows that x * is 200 mm. In addition, the curve in Figure 7 was calculated from the above formula (7) and the conditions of the solid circle mark. It is understood from the relationship shown on the same graph that it is possible to increase the achievable distance of the vibration x * by increasing the impact energy E. For example, the achievable distance of the vibration x * increases by 25%, from 200 mm to 250 mm, by increasing the impact energy E from 40 J to 65 J. In other words, by increasing the impact energy E, it is possible to improve the quality in the central part in the thickness direction of the slab in the proximity of an end portion to the slab width in which central porosity is easily generated due to delayed solidification under complex casting conditions.

5. Relationship of the distance between the trees of the adjacent guide rollers with the achievable distance of impact vibration

Figure 8 is a graph showing a relationship between the impact energy per side per segment and the reachable distance of the vibration, when the distance between the trees of the adjacent guide rollers is varied. Figure 8 is a graph for the case of impact with the same conditions as Figure 7, except for the distance between the trees of adjacent guide rollers AR that is 245 mm or 400 mm. It is understood from the relation shown on the same graph that the achievable distance of the vibration x * increases when the distance between the adjacent guide roller axles AR widens from 245 mm to 400 mm. In other words, in the case of the slab whose proportion between the long side length and the short side length is large, the slab width is large, and the slump between the trees of the adjacent track rollers is easily produced; therefore, it is not possible to take a large distance between the adjacent guide rollers AR. On the other hand, in the case of the slab whose proportion between the long side length and the short side length is small (ie, in this case, the slab is referred to as billet), the billet width is narrow and the bulge width between the trees of the adjacent guide rollers is little; therefore, it is possible to adopt a large distance between the trees of the adjacent guide rollers AR, which is advantageous from the point of view of being able to obtain the effect of impacting over a wide range.

6. Effect of impact from both short sides

Figure 9 is a graph showing the influence of impact on each short side surface that is one end across the width of the slab. The same graph defines the horizontal axis as the distance in a direction normal to the short side from the center to the width of the slab, and defines the vertical axis as the displacement 8 of the slab surface in the thickness direction of the slab. The results of the calculation are shown for the impact cases: only the left short side left to the direction of extraction of the slab; only the right short side; and both short sides simultaneously, in which the casting slab is a billet of approximately 400 mm in width, the distance between the adjacent guide rollers AR is 400 mm, and an impact energy per side per segment is of 45 J. It is understood from the results shown in the same graph that, when combining the left side impact displacement ^8l which is the displacement in one thickness direction of the slab in the case of impact only on the left short side with respect to the extraction direction and the right side impact displacement ^{8 r} which is the displacement in the slab thickness direction in the case of impact only on the right hand side on the right side, the result becomes equivalent to the displacement ^{8 d} in the thickness direction of the slab in the case of impacting both short sides of the slab at the same time.

In the case of impact only on the left short side with respect to the extraction direction or only on the right short side, the horizontal length of the territory in which the displacement 8 in the direction of slab thickness is at least 0, 10 mm, it is approximately 300 mm, which is the length across the width of slab in a normal direction towards the short side, and the displacement 8 can not be made at least 0.10 mm over the entire width. However, by simultaneously impacting the short sides on both sides, the displacement 8 can be made at least 0.10 mm over the entire width of the impact position. Furthermore, as understood from FIG. 9, in the case of simultaneous impact on both short sides, a maximum value of displacement 8 in the central part in the thickness direction of the slab reaches 0.40 mm, and therefore both the displacement 8 can be dramatically increased, and it is possible to achieve a further improvement in the internal quality of the casting slab.

Industrial applicability

According to the method of the present invention, since impacting on the short-side slab surface causes a vibration having a displacement of the long side slab surface of at least 0.10 mm over a wide range of the slab, segregation and / or central porosity is reduced, and therefore a slab that excels in interior quality can be obtained. Therefore, the method of the present invention can be widely applied as a continuous casting method for molding slabs of preferable indoor quality.

List of reference signs

1: immersion dip, 2: cast steel surface (meniscus), 3: mold, 4: molten steel, 5: solidified surface area, 6: guide roller, 7: cast iron, 7a, 7b, 7c, 7d: cast iron sample, 8: impact vibration equipment, 9: block, 10: drive part.

Claims (2)

A continuous steel casting method in which a slab having a rectangular cross-section is molded at the same time that vibration is caused in the slab with a liquid core by arranging at least one pair of impact equipment by vibration in both surfaces of short side of the slab and continuously impacting said surfaces, characterized in that : a vibration energy, a distance between the trees of the adjacent guide rollers and a liquid core thickness are adjusted, such that the impact of the short-sided surface causes a displacement curve 8 (x) of the slab surface long side in the direction of slab thickness as defined by the following formulas (1) and (2) to intersect with a straight line 8 (x) = 0.10 mm in two locations, and a distance from the intersection plus remote from the origin of coordinates in the slab thickness direction, which represents the distance from an impact position on the short side of the slab, is at least 200 mm; Y it hits the short side, 6 (x) - exp [.. 1.5 x {ln (x / (20Ox (AR / ARo) ° 587))} 2 *] * 5max (1) 5 max = Lo x (E / Eo) ° 5 x (AR / AR0) x (t / t0) ° 446 (2) where each symbol in formulas (1) and (2) is indicated as follows, x is a distance (mm) in the slab thickness direction, the impact position being on the short side of slab 0, 8 (x) is a displacement (mm) of the slab surface in the slab thickness direction at the x position, 8max is the maximum displacement (mm) in the slab thickness direction, AR is a distance between the trees of the adjacent guide rollers (mm) in the position where it impacts on the short side, E is the impact energy per side per segment (J), and t is a liquid core thickness of the slab in the impact position on the short side of the slab (mm), where the constants are defined as E ⁰ = 39 (J), AR ⁰ = 245 (mm), fe = 26 (mm), and L ⁰ = 0.114 (mm). 2. The steel continuous casting method according to claim 1, characterized in that in addition the same time phase is used to impact cyclically on the opposite left and right short sides of the slab, in such a way that the displacements 8 (x ) generated by impacting on the left and right short sides, respectively, are combined with each other, and the resultant displacement 8 (x) combined in this way is at least 0.10 mm over the entire width of the slab at the impact positions.